Temperature control system

ABSTRACT

A system including: (i) a semiconductor device; (ii) a thermoelectric controller for controlling the temperature of the semiconductor device; (iii) an electrical power supply for powering the thermoelectric controller; (iv) a first device capable of determining both a direction and a magnitude of current through the thermoelectric controller; (v) a second device also capable of determining a magnitude of current through the thermoelectric controller; and (vi) a controller for controlling the first and second devices on the basis of an electrical indicator of the temperature of the semiconductor device so as to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of power consumption lower than could be achieved using the first device alone.

FIELD OF THE INVENTION

The present invention relates to a technique for controlling the temperature of a device, particularly a laser.

BACKGROUND OF THE INVENTION

Laser diodes are widely used for optical communications. However, the optical output properties of laser diodes can be dependent on temperature, and to maintain a stable optical output the temperature of the laser may need to be regulated. Thermoelectric coolers (also known as Peltier devices) are often used to regulate the temperature of laser diodes. A thermoelectric cooler (TEC) is a solid state heat-pump, whereby, when a current is passed through the TEC, heat is transferred from one side of the TEC to the other, producing a cold side and a hot side. A component such as a laser diode mounted on the cold side can therefore have heat transferred away from it to the hot side, from where it can be dissipated. In addition to being used as coolers, TECs can also be used to heat a component by reversing the direction of the current through the TEC. A TEC is therefore useful in applications where a temperature must be maintained, as can be the case with laser diodes.

In order to maintain a temperature, the TEC current needs to be controlled. In particular, the direction of the current must to be controlled in order to determine the direction of heat transfer, and the magnitude of the current must be controlled in order to determine the rate of the heat transfer.

A known TEC control system 100 for controlling the temperature of a laser diode is shown in FIG. 1. The system 100 controls the operation of a TEC 102 using an H-bridge circuit comprising four MOSFETs (104, 106, 108, 110). The H-bridge allows the direction of the current through the TEC 102 to be controlled. For example, if MOSFETs 104 and 110 are “switched on” (i.e. in a conducting state) and MOSFETs 106 and 108 are “switched off” (i.e. non-conducting), then current can flow from a fixed input voltage VIN 112, through the TEC via MOSFET 104 and 110 to ground. Therefore, the current flows from left to right through the TEC as seen in FIG. 1. Alternatively, if MOSFETs 106 and 108 are switched on and MOSFETs 104 and 110 are switched off, then the current flows from right to left through the TEC, as seen in FIG. 1. Therefore, by controlling the MOSFETs in the H-bridge, the direction of current through the TEC can be controlled.

The system 100 utilizes a temperature sensor 114 mounted on the side of the TEC on which the laser diode 124 is mounted to monitor the temperature of the TEC 102. The signal indicative of the temperature of the laser diode produced by the temperature sensor 114 is converted to digital data by an analogue to digital converter 116. The digital signal indicative of the temperature of the TEC 102 is then input to a microprocessor 118. The microprocessor 118 uses this reading of the TEC temperature to control the currents through the TEC 102, in order to maintain the temperature. The microprocessor 118 controls the current through the TEC 102 by using digital to analogue converters (DACs) 120, 122 to control the MOSFETs of the H-bridge. The microprocessor 118 provides a digital signal to the DACs 120 and 122, which convert this to an analogue voltage level that is applied to the gate terminal of the MOSFETs. The magnitude of the analogue voltage level controls the extent to which the MOSFETs are switched on. A voltage applied to the gate of the MOSFET that is lower than the voltage required to switch the MOSFET to full conduction will allow the MOSFET to conduct, but it will have a resistance related to the value of the gate voltage. Hence, the MOSFETs are controlled to provide variable levels of resistance, and thereby control the magnitude as well as the direction of the current through the TEC 102.

The MOSFETs in the H-bridge are arranged such that MOSFETs 104 and 106 are N-channel MOSFETs (NMOS) and MOSFETs 108 and 110 are P-channel MOSFETs (PMOS). By utilising this configuration, the H-bridge can be controlled with two signals from the microprocessor, as the same signal can be applied to the gates of an N-channel and P-channel MOSFET. A signal to activate the N-channel MOSFET will correspondingly deactivate the P-channel MOSFET and vice versa. Therefore, when the signal from the DAC 120 or 122 is such that N-channel MOSFET 104 or 106 is activated, P-channel MOSFET 108 or 110 is deactivated. Similarly, when the signal from the DAC 120 or 122 is such that P-channel MOSFET 108 or 110 is activated, N-channel MOSFET 104 or 106 is deactivated, as is required to operate the H-bridge.

SUMMARY OF THE INVENTION

It has been observed that there can be a problem with the TEC control technique shown in FIG. 1. Because there can be variation in the efficiency of individual TECs and also variation in the thermal resistance between individual TECs and their respective heat dissipating devices, such as heatsinks, the supply voltage VIN 112 is generally set relatively high so as to be able to provide the necessary rate of heat transfer even for the worst-case scenario such as where both the efficiency and the thermal resistance for the individual TEC are as poor as might be expected and where the operating conditions are as severe as might be expected. Accordingly, for individual TECs for which the efficiency and/or thermal resistance is not so poor and/or where the operating conditions are not at their severest, the MOSFETs (104, 106, 108, 110) in the H-bridge are operated as resistive elements in a partially-on state in order to limit the magnitude of the current through the TEC, and as a consequence of such operation dissipate relatively large amounts of power.

The power dissipated in the MOSFETs leads to an increase in the temperature of the substrate under the TEC, thereby making it more difficult for the TEC to cool the thermal load. Furthermore, the power dissipated in the MOSFETs also increases the overall power dissipation for a module comprising the TEC control system of FIG. 1, which can be an important factor in low-power systems.

It is an aim of the present invention to provide a new type of TEC control, which can at least alleviate this problem.

According to one aspect of the present invention, there is provided a system including: (i) a semiconductor device; (ii) a thermoelectric controller for controlling the temperature of the semiconductor device; (iii) an electrical power supply for powering the thermoelectric controller; (iv) a first device capable of determining both a direction and a magnitude of current through the thermoelectric controller; (v) a second device also capable of determining a magnitude of current through the thermoelectric controller; and (vi) a controller for controlling the first and second devices on the basis of an electrical indicator of the temperature of the semiconductor device so as to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of power consumption lower than could be achieved using the first device alone.

In a preferred embodiment, the semiconductor device is a laser.

In one embodiment, the second device is a DC-DC converter.

In one embodiment, the first device comprises first, second, third and fourth transistors; said first and second transistors are connected in parallel to the power supply in parallel with the third and fourth transistors; and wherein the first and third transistors are connected in series to the thermoelectric controller and the second and fourth transistors are also connected in series to the thermoelectric controller.

In one embodiment, the controller is a microprocessor and controls the second device and the first, second, third and fourth transistors via respective digital-analogue converters.

According to another aspect of the present invention, there is provided a method for controlling the temperature of a semiconductor device using a thermoelectric controller, using a first device capable of determining both a magnitude and a direction of current through the thermoelectric controller; the method including the steps of providing a second device also capable of determining a magnitude of current through the thermoelectric controller, and controlling the first and second devices to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of electric power consumption lower than could be achieved using the first device alone.

According to another aspect of the present invention, there is provided a system including: (i) a semiconductor device; (ii) a thermoelectric controller for controlling the temperature of the semiconductor device; (iii) an electrical power supply for powering the thermoelectric controller; (iv) a first device capable of determining the direction of current through the thermoelectric controller; (v) a second device separate from the first device and capable of determining a magnitude of current through the thermoelectric controller; and a controller for controlling the first and second devices on the basis of an electrical indicator of the temperature of the semiconductor device.

According to another aspect of the present invention, there is provided a controller for controlling the temperature of a semiconductor device using a thermoelectric controller, wherein said controller is arranged to control a first device capable of determining both a magnitude and a direction of current through the thermoelectric controller and a second device also capable of determining a magnitude of current through the thermoelectric controller, on the basis of an electrical indicator of the temperature of the semiconductor device so as to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of power consumption lower than could be achieved using the first device alone.

According to another aspect of the present invention, there is provided an electronic circuit for controlling the temperature of a semiconductor device using a thermoelectric controller, the electronic circuit including: a first device capable of determining both a direction and a magnitude of current through the thermoelectric controller; a second device also capable of determining a magnitude of current through the thermoelectric controller; and a controller for controlling the first and second devices on the basis of an electrical indicator of the temperature of the semiconductor device so as to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of power consumption lower than could be achieved using the first device alone.

According to another aspect of the present invention, there is provided a computer program product comprising program code means which when loaded into a computer controls the computer to carry out the method step of claim 5 of controlling the first and second devices to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of electric power consumption lower than could be achieved using the first device alone.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how the same may be put into effect, reference will now be made, by way of example, to the following drawings in which:

FIG. 1 shows a known TEC control system; and

FIG. 2 shows a laser system according to an embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

Reference will first be made to FIG. 2, in which is shown a laser system 200 according to an embodiment of the present invention. The laser system 200 comprises a TEC 102, an H-bridge comprising four MOSFETs (104, 106, 108, 110), a microprocessor 118, two DACs (120, 122) controlling the MOSFETs, and an ADC 116 reading the value of the TEC temperature from a temperature sensor 114 mounted on the side of the TEC on which the laser diode 124 is mounted.

The laser system 200 further comprises a DC-DC converter 202 and a further DAC 204. The DC-DC converter 202 is a high-efficiency device, with an efficiency typically >90% and often produced as an integrated circuit (IC). The DC-DC converter 202 takes as input a DC voltage level (VIN 112 as shown in FIG. 2) and produces a DC output voltage 206. The magnitude of the DC output voltage 206 can be controlled by a control input to the DC-DC converter 202, such that the voltage level applied to the control input of the DC-DC converter 202 determines the voltage level of the DC output voltage 206. The voltage applied to the control input is provided by the output of the DAC 204.

The system 200 shown in FIG. 2 operates as follows. The microprocessor 118 receives an input signal from the temperature sensor 114 via the ADC 116. In response to this input, the microprocessor 118 determines the required direction and rate of heat transfer for the TEC.

The microprocessor 118 determines a value for the supply voltage 206 to provide the desired magnitude of current through the TEC 102, and sends a digital signal to the DAC 204, which generates a corresponding analogue voltage level. This analogue voltage level is applied to the control input of the DC-DC converter. In response to the control input voltage level, the DC-DC converter produces an output voltage 206, which is applied to the H-bridge.

In order to control the direction of the current through the TEC 102, the microprocessor 118 determines which MOSFETs of the H-bridge need to be activated. Digital signals are sent to the DACs 120 and 122, which produce corresponding analogue voltage levels. The output of the DAC 120 is applied to the gates of the MOSFETs 104 and 108, and the output of the DAC 122 is applied to the gates of the MOSFETs 106 and 110. These signals switch the MOSFETs on or off in order to set the direction of current through the TEC 102. For a given gate signal from DAC 120, the NMOS 104 and the PMOS 108 will be in opposite on and off states, and likewise for a given signal from DAC 122, the NMOS 106 and PMOS 110 will also be in opposite on and off states.

Using the TEC control system 200 shown in FIG. 2, the supply voltage 206 applied to the TEC 102 via the H-bridge is varied, and hence the magnitude of the current through the TEC is controlled by adapting the supply voltage, rather than relying on the MOSFETs for doing so. As control of the supply voltage is used to determine the magnitude of the current through the TEC, those MOSFETs that are controlled to be “on” only need to be operated in a “fully on” state. The “fully on” resistance of the MOSFETs is low, with a typical NMOS “fully on” resistance of approximately 50 milliohms (“mΩ”) and a typical PMOS “fully on” resistance of approximately 200 mΩ. Therefore, very little power is dissipated in the MOSFETs, thereby minimising the heat produced and the power consumed.

Since the efficiency of the DC-DC converter 202 is very high, this does not produce significant amounts of heat, and the power consumed by the DC-DC converter 202 is substantially less than that consumed by the MOSFETs in the known system shown in FIG. 1.

The DACs (120, 122, 204) and ADC 116 may be internal to the microprocessor 118, or external devices. The DACs (120, 122) controlling the MOSFETs (104, 106, 108, 110) must be able to produce both a positive and negative voltage sufficient to fully activate either the N-channel or P-channel MOSFETs in the H-bridge.

If the DC-DC converter 202 has a minimum output voltage greater than 0V (for example this may typically be 0.4V), then DACs 120 and 122 are also used to control the amount of the current delivered to the TEC 102 in addition to controlling the direction.

The applicant draws attention to the fact that the present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof, without limitation to the scope of any definitions set out above. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention. 

1. A system including: (i) a semiconductor device; (ii) a thermoelectric controller for controlling the temperature of the semiconductor device; (iii) an electrical power supply for powering the thermoelectric controller; (iv) a first device capable of determining both a direction and a magnitude of current through the thermoelectric controller; (v) a second device also capable of determining a magnitude of current through the thermoelectric controller; and (vi) a controller for controlling the first and second devices on the basis of an electrical indicator of the temperature of the semiconductor device so as to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of power consumption lower than could be achieved using the first device alone.
 2. A system according to claim 1, wherein the semiconductor device is a laser.
 3. A system according to claim 1, wherein the second device is a DC-DC converter.
 4. A system according claim 1, wherein the first device comprises first, second, third and fourth transistors; said first and second transistors are connected in parallel to the power supply in parallel with the third and fourth transistors; and wherein the first and third transistors are connected in series to the thermoelectric controller and the second and fourth transistors are also connected in series to the thermoelectric controller.
 5. A system according to claim 4, wherein the controller is a microprocessor and controls the second device and the first, second, third and fourth transistors via respective digital-analogue converters.
 6. A method for controlling the temperature of a semiconductor device using a thermoelectric controller, using a first device capable of determining both a magnitude and a direction of current through the thermoelectric controller; the method including the steps of providing a second device also capable of determining a magnitude of current through the thermoelectric controller, and controlling the first and second devices to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of electric power consumption lower than could be achieved using the first device alone.
 7. A system including: (i) a semiconductor device; (ii) a thermoelectric controller for controlling the temperature of the semiconductor device; (iii) an electrical power supply for powering the thermoelectric controller; (iv) a first device capable of determining the direction of current through the thermoelectric controller; (v) a second device separate from the first device and capable of determining a magnitude of current through the thermoelectric controller; and a controller for controlling the first and second devices on the basis of an electrical indicator of the temperature of the semiconductor device.
 8. A controller for controlling the temperature of a semiconductor device using a thermoelectric controller, wherein said controller is arranged to control a first device capable of determining both a magnitude and a direction of current through the thermoelectric controller and a second device also capable of determining a magnitude of current through the thermoelectric controller, on the basis of an electrical indicator of the temperature of the semiconductor device so as to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of power consumption lower than could be achieved using the first device alone.
 9. An electronic circuit for controlling the temperature of a semiconductor device using a thermoelectric controller, the electronic circuit including: a first device capable of determining both a direction and a magnitude of current through the thermoelectric controller; a second device also capable of determining a magnitude of current through the thermoelectric controller; and a controller for controlling the first and second devices on the basis of an electrical indicator of the temperature of the semiconductor device so as to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of power consumption lower than could be achieved using the first device alone.
 10. A computer program product comprising program code means which when loaded into a computer controls the computer to carry out the method step of claim 6 of controlling the first and second devices to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of electric power consumption lower than could be achieved using the first device alone. 